The present invention is directed, in general, to wireless networks and, more specifically, to a system for selectively reconfiguring radio channels to recover from an overhead channel failure in wireless network base station.
The quality of service provided by a base station (BS) in a wireless network is greatly influenced by the reliability and the redundancy of the radio resources responsible for carrying out communications between the base station and the mobile stations (e.g., cell phones, wireless modem-equipped computers, etc.) In the cell site covered by the base station, one of the most crucial components of a base station is the channel card. The channel card contains the channel elements that transmit and receive RF signals used to communicate with the mobile stations.
A channel element may be configured to operate as a traffic channel or as an overhead channel. Traffic channels carry the actual voice (or data) signals transmitted to and received from the mobile stations during a conversation (or a data transfer) Overhead channels carry the control signals that are used to establish traffic channels and, frequently, to break down the traffic channels.
There are four types of overhead channels: pilot, synchronization (xe2x80x9csyncxe2x80x9d), access, and paging. The pilot channel provides a means by which a mobile station may lock onto and acquire a BTS, provides timing reference for the system, and provides signal strength indications. The sync channel provides a mobile station with timing information necessary to synchronize with the system and also provides the following data: system time, long code state, protocol revision, paging channel data rate, and the like. The access channel allows a mobile station to communicate with the base station when the mobile station is not involved in a call. The mobile station uses the access channel when the mobile station responds to a paging message sent by the base station or when the mobile station originates a call. The paging channel provides a means of communication with a mobile station when the mobile stat on is not involved in a call. The paging channel is used to deliver system-wide configuration information, as well as messages that are specific messages to a particular mobile.
In some wireless network configurations, each of the pilot, sync, access and paging overhead channels are separately configured on individual channel elements. In other wireless network configurations, one or more of the overhead channels may be configured together on one, two, or three channel elements. Generally, however, a minimum of two channel elements are used to provide the overhead channels: the paging channel is configured by itself on one channel element, and the pilot, sync and access channels are configured on one two, or three other channel elements.
Frequently, the cell covered by a base station is divided into, for. example, three sectors of 120 degree each. Each sector has its own pilot, sync, access and paging channels. Assuming that only one access channel and one paging channel are configured per sector, each sector requires between two and four channel elements to provide overhead channels, depending on whether overhead channels are combined. Thus, assuming still that only one access channel and one paging channel are configured per sector, a three-sector base station may use anywhere between six and twelve channel elements to provide overhead channels. If more than one access channel and/or paging channel are configured, even more channel elements are required to provide overhead channels.
Since the overhead channels are essential to establishing and maintaining the traffic channels, failure of an overhead channel will have detrimental effects upon both existing calls and incoming calls unless a proper recovery procedure is immediately executed after the failure occurs. Prior art wireless networks typically execute one of the following overhead channel recovery procedures:
1. No Recovery
In some systems, no automated recovery procedure is used. If an overhead channel fails, system alarms are triggered that send a notice to system operators informing them of the failure. At that time, a service technician is dispatched to repair or replace the non-functioning channel card, signal processor, channel element, etc. In the interim, however, the base station is partially or completely crippled. The disadvantages with this implementation are obvious. Any overhead failure at least partially disrupts the services provided by the wireless network. Voice packets may be lost, resulting in degraded voice quality. Even worse, calls may be lost completely if mobile stations are unable to detect the base station""s signals.
2. Standby Scheme
In some systems, a xe2x80x9cstandbyxe2x80x9d channel element is reserved specifically for overhead channel recovery procedure. A standby overhead channel can be reserved for any of the overhead channels, but it is more common. to reserve the standby channel element for the pilot channel. The disadvantages with this implementation is that the channel element is effectively removed from the resource pool of available channel elements. This reduces by one the number of calls that can be handled by each base station.
3. Traffic Channel Pool Scheme
In some systems, a channel element normally used to carry voice/data traffic (i.e., a traffic channel element) is reallocated by the system from the pool of available traffic channel elements and is reconfigured to replace the failed overhead channel. In the prior art, the traffic channels are organized based on logical location rather than physical location. The allocation process is based on selection of a traffic channel element at the end of the traffic channel element pool. The traffic channel pool scheme increases the system capacity by not wasting a channel element as a standby channel element. The overhead channel recovery still occurs quickly enough to avoid any potential system service interruption.
Each recovery scheme has its own unique advantages, but all three existing schemes share common disadvantages that are not adequately addressed in any particular scheme. One common disadvantage is that it is possible for many or even all of the recovered overhead channels to be reconfigured on the same channel card or even on the same channel digital signal processor (CDSP). If this occurs, a large number of control messages from the overhead channels may overload the DPRAM of the channel card carrying the overhead channels, while allowing the other available channel cards to remain idle. Another common disadvantage is related to the first one. If many or all of the overhead channels have been reconfigured on the same channel card or CDSP and that channel card or CDSP then experiences a failure, the system may be overwhelmed while attempting to reconfigure the overhead channels on other channel elements during failure recovery.
There is therefore a need in the art for a wireless network that suffers minimal performance degradation upon the occurrence of a failure in an overhead channel. In particular, there is a need for a recovery procedure that does not unduly overload any individual piece of base station equipment with a large number of overhead channels. There is a still further need for a wireless network that minimizes the risk of multiple overhead channel failures upon the failure of a single channel card or CDSP in a base station.
To address the above-discussed deficiencies of the prior art, it is a primary objective of the present invention to provide, for use in a wireless network base station, the base station capable of communicating in at least one overhead channel and a plurality of traffic channels with a plurality of mobile stations by means of a plurality of channel elements, an apparatus for recovering from an overhead channel failure comprising: 1) a failure detection circuit capable of detecting a failed overhead channel and generating a failure notification; and 2) a channel allocator capable of receiving the failure notification and, in response thereto, a) identifying a failed one of the plurality of channel elements responsible for the failed overhead channel and a first signal processing device associated with the failed overhead channel element; and b) selecting an available traffic channel element to replace the failed channel element, wherein the available traffic channel element is located on a second signal processing device that is processing a least number of overhead channels thereon.
According to one embodiment of the present invention, the second signal processing device and the first signal processing device comprise distinct digital signal processors.
According to another. embodiment of the present invention, the second signal processing device and the first signal processing device comprise distinct digital signal processors disposed on separate channel card circuits.
According to still another embodiment of the present invention, the least number of overhead channels is zero.
According to yet another embodiment of the present invention, the available traffic channel element is an idle traffic channel element.
According to a further embodiment of the present invention, the second signal processing device and the first signal processing device are disposed on separate channel cards.
According to a still further embodiment of the present invention, the apparatus further comprises a database associated with the channel allocator, wherein the database stores physical device location parameters associated with the plurality of channel elements.
According to a yet further embodiment of the present invention, the channel allocator causes the available channel to be reconfigured as an overhead channel capable of replacing the failed overhead channel.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better. understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the terms xe2x80x9ccontrollerxe2x80x9d and xe2x80x9callocatorxe2x80x9d mean any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller or allocator may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.